Biologics, especially monoclonal antibodies (mAbs), are an increasingly important part of the drug discovery and development portfolio across the pharmaceutical industry. To enable robust demonstration of pillars 1 and 2 [1] for mAbs, specialised assays are required to measure the complex interactions between mAb and target. This is especially important for the interpretation of soluble target interactions. In some instances, multiple assays with overlapping purposes (e.g., developing both complex and total assays) have been developed. In retrospect, these efforts may have led to excessive time and resources spent in assay development and the generation of data that is contradictory or misleading. Our recommendation is to invest resources early into the development of total assays for both mAb and target. Free target assay data may be inaccurate and report higher levels of free target than are present in the sample at collection due to re-equilibrium during measurement. Total assay formats are inherently less sensitive to the effects of sample preparation, assay conditions, and re-equilibration than free or complex assays. It is acknowledged that pathology/pharmacology is ultimately driven by the free target and knowledge of its dynamics are critical. However, generation of appropriate total target data and using model-based estimation of free target concentrations is a more robust approach than utilisation of direct assay derived estimates. Where free data are utilised, the potential biases should be prospectively considered when developing the assay and utilising the data for quantitative analyses.

Biological networks are characterized by diverse interactions and dynamics in time and space. Many regulatory modules operate in parallel and are interconnected with each other. Some pathways are functionally known and annotated accordingly, e.g., endocytosis, migration, or cytoskeletal rearrangement. However, many interactions are not so well characterized. For reconstructing the biological complexity in cellular networks, we combine here existing experimentally confirmed and analyzed interactions with a protein-interaction inference framework using as basis experimentally confirmed interactions from other organisms. Prediction scoring includes sequence similarity, evolutionary conservation of interactions, the coexistence of interactions in the same pathway, orthology as well as structure similarity to rank and compare inferred interactions. We exemplify our inference method by studying host-pathogen interactions during infection of Mus musculus (phagolysosomes in alveolar macrophages) with Aspergillus fumigatus (conidia, airborne, asexual spores). Three of nine predicted critical host-pathogen interactions could even be confirmed by direct experiments. Moreover, we suggest drugs that manipulate the host-pathogen interaction.

The Vitamin D External Quality Assessment Scheme (DEQAS) distributes human serum samples four times per year to over 1000 participants worldwide for the determination of total serum 25-hydroxyvitamin D [25(OH)D)]. These samples are stored at -40 °C prior to distribution and the participants are instructed to store the samples frozen at -20 °C or lower after receipt; however, the samples are shipped to participants at ambient conditions (i.e., no temperature control). To address the question of whether shipment at ambient conditions is sufficient for reliable performance of various 25(OH)D assays, the equivalence of DEQAS human serum samples shipped under frozen and ambient conditions was assessed. As part of a Vitamin D Standardization Program (VDSP) commutability study, two sets of the same nine DEQAS samples were shipped to participants at ambient temperature and frozen on dry ice. Twenty-eight laboratories participated in this study and provided 34 sets of results for the measurement of 25(OH)D using 20 ligand binding assays and 14 liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods. Equivalence of the assay response for the frozen versus ambient DEQAS samples for each assay was evaluated using multi-level modeling, paired t-tests including a false discovery rate (FDR) approach, and ordinary least squares linear regression analysis of frozen versus ambient results. Using the paired t-test and confirmed by FDR testing, differences in the results for the ambient and frozen samples were found to be statistically significant at p < 0.05 for four assays (DiaSorin, DIAsource, Siemens, and SNIBE prototype). For all 14 LC-MS/MS assays, the differences in the results for the ambient- and frozen-shipped samples were not found to be significant at p < 0.05 indicating that these analytes were stable during shipment at ambient conditions. Even though assay results have been shown to vary considerably among different 25(OH)D assays in other studies, the results of this study also indicate that sample handling/transport conditions may influence 25(OH)D assay response for several assays.

This protocol describes how to measure interaction between Notch receptors and their ligands by cell-based assay using Dynabeads. We have used the protocol to determine binding capacity between Notch1-transfected HEK293T cells and ligand-coated Dynabeads. Expression of Eogt in Notch1-expressing cells promoted binding toward DLL4-coated beads, but not JAG1-coated beads. The Notch-ligand assay using Dynabeads suggested that Eogt facilitates DLL4-Notch1 interaction ( Sawaguchi et al., 2017 ).

An interlaboratory comparison study was conducted by the Vitamin D Standardization Program (VDSP) to assess the performance of ligand binding assays (Part 2) for the determination of serum total 25-hydroxyvitamin D [25(OH)D]. Fifty single-donor samples were assigned target values for concentrations of 25-hydroxyvitamin D2 [25(OH)D2], 25-hydroxyvitamin D3 [25(OH)D3], 3-epi-25-hydroxyvitamin D3 [3-epi-25(OH)D3], and 24R,25-dihydroxyvitamin D3 [24R,25(OH)2D3] using isotope dilution liquid chromatography-tandem mass spectrometry (ID LC-MS/MS). VDSP Intercomparison Study 2 Part 2 includes results from 17 laboratories using 32 ligand binding assays. Assay performance was evaluated using mean % bias compared to the assigned target values and using linear regression analysis of the test assay mean results and the target values. Only 50% of the ligand binding assays achieved the VDSP criterion of mean % bias ≤ |± 5%|. For the 13 unique ligand binding assays evaluated in this study, only 4 assays were consistently within ± 5% mean bias and 4 assays were consistently outside ± 5% mean bias regardless of the laboratory performing the assay. Based on multivariable regression analysis using the concentrations of individual vitamin D metabolites in the 50 single-donor samples, most assays underestimate 25(OH)D2 and several assays (Abbott, bioMérieux, DiaSorin, IDS-EIA, and IDS-iSYS) may have cross-reactivity from 24R,25(OH)2D3. The results of this interlaboratory study represent the most comprehensive comparison of 25(OH)D ligand binding assays published to date and is the only study to assess the impact of 24R,25(OH)2D3 content using results from a reference measurement procedure.

An interlaboratory study was conducted through the Vitamin D Standardization Program (VDSP) to assess commutability of Standard Reference Materials® (SRMs) and proficiency testing/external quality assessment (PT/EQA) samples for determination of serum total 25-hydroxyvitamin D [25(OH)D] using ligand binding assays and liquid chromatography-tandem mass spectrometry (LC-MS/MS). A set of 50 single-donor serum samples were assigned target values for 25-hydroxyvitamin D2 [25(OH)D2] and 25-hydroxyvitamin D3 [25(OH)D3] using reference measurement procedures (RMPs). SRM and PT/EQA samples evaluated included SRM 972a (four levels), SRM 2973, six College of American Pathologists (CAP) Accuracy-Based Vitamin D (ABVD) samples, and nine Vitamin D External Quality Assessment Scheme (DEQAS) samples. Results were received from 28 different laboratories using 20 ligand binding assays and 14 LC-MS/MS methods. Using the test assay results for total serum 25(OH)D (i.e., the sum of 25(OH)D2 and 25(OH)D3) determined for the single-donor samples and the RMP target values, the linear regression and 95% prediction intervals (PIs) were calculated. Using a subset of 42 samples that had concentrations of 25(OH)D2 below 30 nmol/L, one or more of the SRM and PT/EQA samples with high concentrations of 25(OH)D2 were deemed non-commutable using 5 of 11 unique ligand binding assays. SRM 972a (level 4), which has high exogenous concentration of 3-epi-25(OH)D3, was deemed non-commutable for 50% of the LC-MS/MS assays.

OBJECTIVE: The purpose of this study was to evaluate the suitability of whole blood microsampling procedures in non-human primate (NHP) to support toxicokinetic assessments of biotherapeutics in non-human primates.
METHODS: A one-month single dose intravenous pharmacokinetic (PK) study was performed in male cynomolgus monkeys with a human IgG1 control monoclonal antibody (mAb) as a surrogate monoclonal antibody biotherapeutic. In this study, both serum samples (conventional sample collection) and microsampling samples were collected. Microsampling samples were collected from two sites on cynomolgus monkey, with each site using two different devices for the whole blood collection. The drug concentrations from all sample types were determined using a quantitative ligand binding assay (LBA). The PK parameters obtained from microsampling samples and serum samples were examined using a standard PK analysis method. The comparability of key PK parameters from both sample types were analyzed statistically.
RESULTS: Similar profiles of drug concentrations versus timepoints from all sampling procedures were observed. The correlations of PK concentration data obtained from serum and microsampling samples were ≥ 0.97 using Brand Alman Plot analysis. The key PK parameters obtained from microsampling samples were comparable to those obtained from serum samples (the % differences of mean PK parameters obtained from both sample types were within ±25%).
CONCLUSIONS: This study confirmed that PK parameters obtained from samples using microsampling were comparable to that of serum samples in cynomolgus monkeys. Therefore, the microsampling procedure described can be used as a substitute for conventional sampling procedure to support PK/TK studies of biotherapeutics in non-clinical product developments.

BACKGROUND: Neural Cell Adhesion Molecule 1 (NCAM-1), a multifunctional member of the immunoglobulin superfamily, is expressed on the surface of neurons, glia, skeletal muscle, and natural killer cells. NCAM-1 has been implicated as having a role in cell-cell adhesion, involved in development of the nervous system, and for cells involved in the expansion of T cells and dendritic cells which play an important role in immune surveillance. Sensitive and specific methods to quantify non-surface bound NCAM-1 are not available.
METHODS: A sandwich ligand binding assay was developed for quantification of NCAM-1 in plasma and validated using an electro-chemiluminescent (ECL) technology.
RESULTS: The data presented here demonstrated that the validated method met all prespecified criteria for precision, linearity, and accuracy in the range of 62.5 ng/mL to 4000.0 ng/mL, the range believed to be most relevant for plasma. The bioanalytical validation of the assay established the inter-assay coefficient of variation <8 % for calibration points, <2 % for high quality control (HQC), <8 % for medium quality control (MQC) and <19 % for low quality control (LQC) samples. Purified NCAM-1 spike-recovery experiment in plasma was used to determine assay accuracy; nominal concentrations (%) of NCAM-1 ranged from 91 % to 112 % for high and low spike level, respectively. Assay performance was subsequently evaluated for parallelism, selectivity, interference, and stability.
CONCLUSIONS: NCAM-1 assay has been developed and validated in human plasma and met all assay validation parameters pre-determined during development. Clinical testing of human plasma samples indicated that NCAM-1 does not seem to be influenced by age and was slightly influenced by gender. NCAM-1 assay has potential to be used as a biomarker assay once the assay is subjected to appropriate clinical assessment and diagnostic thresholds are established.

Sensitive and reproducible pharmacokinetic (PK) assays and immunogenicity assessment are required as part of the complex and lengthy development process for biotherapeutic proteins. Ligand binding assays (LBAs) are included in a range of approaches applied to understand the nature and properties of the drug as well as the induction of anti-drug antibodies (ADA) against the therapeutic, which can cause adverse events and loss of efficacy. Currently, most biotherapeutics are monoclonal human or humanized antibodies. Anti-idiotypic antibodies, targeting the idiotopic determinants of individual antibody drugs are recognized as perfect reagents for such LBAs. Here we describe the typical setups for these assays and how different types of anti-biotherapeutic antibodies can be used to establish selective and sensitive assays.

Hyphantria cunea (Drury) is a destructive invasive pest species in China that uses type II sex pheromone components. To date, however, the binding mechanisms of its sex pheromone components to their respective pheromone-binding proteins (HcunPBPs 1/2/3) have not been explored. In the current study, all three HcunPBPs were expressed in the antennae of both sexes. The prokaryotic expression and ligand binding assays were employed to study the binding of the moth\'s four sex pheromone components, including two aldehydes and two epoxides, and 24 plant volatiles to the HcunPBPs. Our results showed that the abilities of these HcunPBPs to bind to the aldehydes were significantly different from binding to the epoxides. These three HcunPBPs also selectively bind to some of the plant volatiles tested. Our molecular docking results indicated that some crucial hydrophobic residues might play a role in the binding of HcunPBPs to their sex pheromone components. Three HcunPBPs have different selectivities for pheromone components with both major and minor structural differences. Our study provides a fundamental insight into the olfactory mechanism of moths at the molecular level, especially for moth species that use various type II pheromone components.